Re: [PATCH v6 3/4] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter
From: xiakaixu <hidden>
Date: 2015-08-06 02:49:51
Also in:
lkml
于 2015/8/5 21:53, Peter Zijlstra 写道:
quoted hunk ↗ jump to hunk
On Wed, Aug 05, 2015 at 12:04:25PM +0200, Peter Zijlstra wrote:quoted
Also, you probably want a WARN_ON(in_nmi()) there, this function is _NOT_ NMI safe.I had a wee think about that, and I think the below is safe. (with the obvious problem that WARN from NMI context is not safe) It does not give you up-to-date overcommit times but your version didn't either so I'm assuming you don't need those, if you do need those it needs more but we can do that too. --- include/linux/perf_event.h | 1 + kernel/events/core.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 54 insertions(+)diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 2027809433b3..64e821dd64f0 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h@@ -659,6 +659,7 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, void *context); extern void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu); +extern u64 perf_event_read_local(struct perf_event *event); extern u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running);diff --git a/kernel/events/core.c b/kernel/events/core.c index 39753bfd9520..7105d37763c1 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c@@ -3222,6 +3222,59 @@ static inline u64 perf_event_count(struct perf_event *event) return __perf_event_count(event); } +/* + * NMI-safe method to read a local event, that is an event that + * is: + * - either for the current task, or for this CPU + * - does not have inherit set, for inherited task events + * will not be local and we cannot read them atomically + * - must not have a pmu::count method + */ +u64 perf_event_read_local(struct perf_event *event) +{ + unsigned long flags; + u64 val; + + /* + * Disabling interrupts avoids all counter scheduling (context + * switches, timer based rotation and IPIs). + */ + local_irq_safe(flags);
s/local_irq_safe/local_irq_save, and I have compiled and tested this function and it is fine. Will use it in the next set. Thanks.
+
+ /* If this is a per-task event, it must be for current */
+ WARN_ON_ONCE((event->attach_state & PERF_ATTACH_TASK) &&
+ event->hw.target != current);
+
+ /* If this is a per-CPU event, it must be for this CPU */
+ WARN_ON_ONCE(!(event->attach_state & PERF_ATTACH_TASK) &&
+ event->cpu != smp_processor_id());
+
+ /*
+ * It must not be an event with inherit set, we cannot read
+ * all child counters from atomic context.
+ */
+ WARN_ON_ONCE(event->attr.inherit);
+
+ /*
+ * It must not have a pmu::count method, those are not
+ * NMI safe.
+ */
+ WARN_ON_ONCE(event->pmu->count);
+
+ /*
+ * If the event is currently on this CPU, its either a per-task event,
+ * or local to this CPU. Furthermore it means its ACTIVE (otherwise
+ * oncpu == -1).
+ */
+ if (event->oncpu == smp_processor_id())
+ event->pmu->read(event);
+
+ val = local64_read(&event->count);
+ local_irq_restore(flags);
+
+ return val;
+}
+
static u64 perf_event_read(struct perf_event *event)
{
/*
.